1. Field of the Invention
The invention relates to a welding method for producing a component from two or more constructional elements made of a metallic material, in particular of an oxide dispersion-hardened alloy based on nickel or iron, and with insertion of a metallic interlayer are joined together.
2. Description of the Prior Art
Such a method is used in particular in the manufacture of components produced from oxide dispersion-hardened alloys. Rotor and stator blades and gas turbine segments in which there is a build-up of heat can be manufactured from these alloys.
The formation of components from an oxide dispersion-hardened alloy begins with the production of the alloy-forming powder. The metals or metal compounds used in producing the powder are alloyed mechanically in a high-energy mill. From the powder obtained in this manner, blanks are first produced by means of extrusion. These blanks are further processed to the final components by forging, rolling and/or machining.
The special feature of these oxide dispersion-hardened alloys, in addition to the oxide dispersion and possible .gamma.-precipitation, is an oriented grain structure which results from recrystallization. However, a disadvantage of this is that components cannot be case from the alloy and joined together using the conventional fusion welding method. Components which are to have, for example, flow-through channels in their center must be manufactured from at least two constructional elements. Before they are joined together, these constructional elements are provided with depressions, in particular by forging and, after the two halves have been joined together, these depressions form the desired channels which are required to the passage of cooling liquids. Firmly bonding the constructional elements to give such a component is not completely without difficulty.
Joining together constructional elements of dispersion-hardened materials still in their finely divided state by means of diffusion welding to give the desired component has been described. Diffusion welding is carried out using parameters with which the formation of coarse grains is avoided and the energy for subsequent recrystallization is retained. Any oriented recrystallization which takes place over the temperature gradient beyond the joined surface occurs after welding. The disadvantage of this method is the high plasticity of the components, since these are not yet in the recrystallized form when the diffusion welding is carried out. As a result of the pressure required for diffusion welding, it is very difficult to leave the cooling channels in an undeformed state in the center of the component to be formed. Additional measures have to be taken in order to retain the shape of these cooling channels during the diffusion welding. To date, it has not been possible to carry out joining in an economical and well-defined way without undesirable deformation of these channels. On the other hand, it is also impossible to solder inserts into the depressions suitable for preventing deformation of the depressions during diffusion welding, since all soldering processes which are carried out at below 1,000.degree. C. result in remelting during recrystallization annealing.
Furthermore, it is known that components made of oxide dispersion-hardended alloys can be joined, after recrystallization, using a high-temperature solder. However, this method does not give a completely integrated weld seam, so that the soldered area constitutes a weak point with poorer mechanical properties.